I have a fifth wheel with Goodyear G614 G rated tires. They still have very good tread and still look good but they were made in the 19th week of 2014. I read that you can go between 6 to ten years....
I replaced my 17.5 GY G114's last May that were produced late 2014 strictly due to age. They had about 22k miles on them and looked like new. I just didn't want to chance it based on the "age-out" theories.